Reputable

Ive seen some benchmarks where the radeon does better, yet it costs around 200$ less tun the Geforce Gtx.. Can someone shine some light onto this as to which one will offer better performance? My monitor is a 144Hz 1080p.

Reputable

If you're using an ASUS VG248QE than you will want to go with the EVGA GTX 780Ti Dual Classified http://www.amazon.com/gp/product/B00H9ZRCBO. The 780Ti performs better at 1440p resolutions or below and if you have the VG248QE, it's hardware optimized to work better with nVidia cards.

It will not do 3D with AMD cards and can only perform over 60Hz with AMD cards through the Dual-Link DVI connection and cannot perform over 60Hz in Eyefinity. Go with the 780Ti.

"Moving up to 2560x1440, the wider memory bus of the dual 290 products becomes more important, putting the GTX 780 under further pressure."

Honestly, the $200 extra price mark really doesn't justify itself.
The R9 290x has more VRAM so at 1440p where VRAM matters, the 290x is a better choice in my opinion. Also, because of its higher VRAM it will be better in the future because games seem to suck VRAM up and even though demanding games at the moment average 2-2.5GB of VRAM usage, they get close to 3GB, so in the future this could be your limitation with the 780ti... Also, with mantle being integrated into multiple games, it will have a definite dominance over the 780ti in the future...

Why pay $200 more for similar performance (or worse) and less VRAM?
I'm aware that nvidia have certain features that a lot of people like, but that really doesn't justify the massive price gap between the cards. nvidia clearly overprice their cards... take the R9 295X2 and the Titan Z for example. The Titan Z is twice the price of the AMD and yet has similar performance.

"Moving up to 2560x1440, the wider memory bus of the dual 290 products becomes more important, putting the GTX 780 under further pressure."

Honestly, the $200 extra price mark really doesn't justify itself.
The R9 290x has more VRAM so at 1440p where VRAM matters, the 290x is a better choice in my opinion. Also, because of its higher VRAM it will be better in the future because games seem to suck VRAM up and even though demanding games at the moment average 2-2.5GB of VRAM usage, they get close to 3GB, so in the future this could be your limitation with the 780ti... Also, with mantle being integrated into multiple games, it will have a definite dominance over the 780ti in the future...

Why pay $200 more for similar performance (or worse) and less VRAM?
I'm aware that nvidia have certain features that a lot of people like, but that really doesn't justify the massive price gap between the cards. nvidia clearly overprice their cards... take the R9 295X2 and the Titan Z for example. The Titan Z is twice the price of the AMD and yet has similar performance.